If the first value in the set is null, then the function returns null until we specify IGNORE NULLS

If we specify IGNORE NULLS,then First_Value function returns the first non-nullable value else it returns all null values.

All Above

It is an analytic function.It returns the first value from the order set of values.
If the first value in the set is null, then the function returns null until we specify IGNORE NULLS.
However, if we specify IGNORE NULLS,then First_Value function returns the first non-nullable value else it returns all null values.